Factors affecting the nutritional quality of soya products

Publisher Website
Google Scholar
Abstract
The nutritional quality of soya products is determined not only by the quantity and availability of the amino acids which make up the protein of such products, but is also markedly affected by the processing conditions which are employed in their manufacture. The most important factor in this regard is the application of some form of heat treatment which serves to inactivate a number of naturally occurring constituents of the soybean. Although non‐toxic in the truest sense of the word, these are substances which can nevertheless elicit adverse physiological responses in animals, and, unless destroyed, can detract from the full nutritional potential of soya protein. The best known and certainly the most studied of these factors are the inhibitors of trypsin and chymotrypsin, enzymes which play a key role in the digestion of proteins in animals. These will be discussed with respect to their possible model of action in vivo, and an attempt will be made to evaluate their nutritional significance in man. Also present in soybeans are several other heat‐labile components whose physiological significance is less well understood. These include the phytohemagglutinins (lectins), goitrogens, antivitamins and phytates. Less sensitive to the destruction effects of heat are a number of factors which are capable of producing a wide variety of physiological responses in animals and include saponins, estrogens, oligosaccharides and allergens. Although present in readily detectable quantities, their effect on the nutritional quality of soya protein is questionable. Not to be overlooked is the fact that harsh processing conditions such as excessive heat treatment or extraction under alkaline conditions may lead to the destruction of economic importance at the present time, brief consideration will be given to the possible effects of germination and fermentation on the nutritive quality of the protein resulting from such treatments.